diff --git a/homeassistant/components/calendar/strings.json b/homeassistant/components/calendar/strings.json
index 2663408cfdb..898953c18ac 100644
--- a/homeassistant/components/calendar/strings.json
+++ b/homeassistant/components/calendar/strings.json
@@ -9,7 +9,11 @@
       },
       "state_attributes": {
         "all_day": {
-          "name": "All day"
+          "name": "All day",
+          "state": {
+            "true": "[%key:common::state::yes%]",
+            "false": "[%key:common::state::no%]"
+          }
         },
         "description": {
           "name": "Description"